The most common repotting mistake isn't technique, it's timing — moving a plant into a new pot far more often than it needs.
A plant is generally ready for a larger pot when roots are visibly circling the inside of the nursery pot, growing out of the drainage hole, or when the plant needs watering unusually often because there's more root than soil left to hold moisture. Absent those signs, an annual repot isn't necessary and can do more harm than good, especially to slow growers like ZZ plants, which actually prefer being slightly snug.
When it is time, go up only one pot size — roughly two inches in diameter larger than the current pot. A pot that's dramatically bigger holds far more soil than the roots can use, and that excess soil stays wet long after the plant needs water, which is a common cause of root rot after a well-intentioned repot.
Gently loosen circling roots at the bottom and sides before setting the plant in new mix, water it in well, and expect a short adjustment stall — a week or two of little visible growth is normal and not a sign of failure.
The best time to repot most houseplants is during active growth, spring into summer, rather than winter, when roots recover more slowly from any disturbance.